1. Field of the Invention
This invention pertains to bit and sleeve assemblies for rock drill heads or the like and to methods of installing the combined bit and sleeve assembly in a head.
2. Description of the Prior Art
As stated in my earlier application, one of the problems with prior art rock drilling heads is that the bits in many cases are not replaceable resulting in the necessity of replacing the entire head at a cost of several times the cost of the individual bit when only a few bits are actually in need of replacement. One prior art attempt at providing replaceable bits was unsuccessful since the bits were difficult to remove, often became loose, and in some cases caused cracking of the head under percussive loading. This prior art technique employed bits mounted in sleeves which were fitted in bores in the head assembly. These sleeves were split so that they expanded against the inside wall of the bores. The bores were provided of necessity with an internal central opening accessible from the interior of the head assembly so that a worn sleeve and bit could be driven out from within. The placement of the bits in the head was thus primarily determined by the availability of access from within the head to drive out the bits and was not designed for optimum drilling configurations. Furthermore, the necessity of numerous access holes weakened the structure of the head assembly. Still further, the sleeves did not firmly hold the bit in the head and under percussive loading the bits would become loosened or broken.
Other prior art attempts at replacing the bits without the use of sleeves have proven extremely expensive since the bits are difficult to machine to the exact tolerances of the bores in the head and often fractured the metal around the bore when being pressed into the bore. In addition, the percussive loading on the bits is transmitted directly to the edges of the bores, causing damage of the edges and requiring that a bore be recut to a larger size before a replacement bit can be installed. Furthermore, the replacement bit is then an odd size making it expensive to manufacture.